Numerical investigation on shear mechanical characteristics of rock joints filled with clay-rich fillings

The clay filling layer can significantly influences the shear behavior of rock joints. In this study, a numerical model for the direct shear test on clay-rich filling rock masses under constant normal stress was developed using the Continuum Discontinuum Element Method (CDEM), and validated through compression-shear experiments. Subsequently, the influence mechanism of water content and various normal stresses on the shear behavior of rocks were systematically examined. From a microscopic perspective, the damage evolution of rough joint surfaces under different water contents and normal stresses was quantitatively assessed. Finally, numerical results were compared against theoretical models. The research results indicate that the CDEM can effectively simulate the nonlinear mechanical behaviors of rock joints containing clay-rich filling layers during shearing process, and it fits well with the experimental results. The peak shear strength decreases as water content increases, while it increases with the increase of normal stress. The normal stress would change the maximum static friction force when the filling layer slides, while water content would change the friction angle between the filling material particles, both of which affect the peak shear strength of the rock joint. Additionally, it was compared with the strength criteria obtained from the experiments, and the comparison results are consistent.